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Old Timekeeper, New Battery Technology

One of humankind’s oldest technologies for keeping time has provided the inspiration for one of the newest ways of storing and retrieving energy. The old-fashioned hourglass was the model for a new type of battery that could help make power from renewable energy sources widely viable.

The new liquid battery, which uses a passive, gravity-fed arrangement, could offer great advantages over other battery designs because it is simple and inexpensive, say the MIT researchers who have made a demonstration version.

Liquid flow batteries—in which the positive and negative electrodes are each in liquid form—are not a new concept. The basic technology can use a variety of chemical formulations, but its key components are tiny particles that can be carried along in a liquid slurry. Increasing storage capacity simply requires bigger tanks to hold more of the slurry.

Previous versions of liquid flow batteries have relied on tanks, valves, and pumps, adding to the cost and leading to leaks and failures. But the new gravity-fed version eliminates that complexity. The rate of energy production can be adjusted simply by changing the angle of the device to speed up or slow down the rate of flow. The flow can then be reversed by turning the device over.

In this design, the shape looks more like a rectangular window frame than a traditional hourglass, with a narrow slot at the place where two sashes would meet in the middle. While a conventional, all-solid battery requires electrical connectors for each cell in a large battery system, in the flow battery only the “neck” of the hourglass requires these contacts, greatly simplifying its assembly.

In the proof-of-concept version built by materials science professor Yet-Ming Chiang ’80, ScD ’85, and his team, only one of the battery’s two sides is composed of flowing liquid, while the other side—a sheet of lithium—is in solid form. The team next plans to make a version where both sides are liquid and flow side by side through an opening, separated by a membrane.

The new design should make possible simpler and more compact battery systems, which could be inexpensive and modular. This could allow for gradual expansion of grid-connected storage systems to meet growing demand, Chiang says, which could be useful for scaling up the use of intermittent power sources such as wind and solar.